Major Component of Electrical Control systems

Actions in facilities and processing operations are ACTIVATED by some elements or components reffered to as input and output devices. Logics are built behind the scenes of all control operation irrespetive of design, complexity and application. Either to light a single but or to control a robot arm. For control actions to take place, components are interconnected to carry out various control actions following predesigned logics which examines different set conditions that defines a particular or intended operation(s).
Therefore before we dive into control concepts, components that are put together to achieve several applications needed to be considered and there usage also clearly understood.

List of electrical control components

Switch: Switches are input devices and they are used for giving a HIGH or  LOW signal in an electrical circuit. Simply say for turning ON or OFF a signal level in a circuit. The term switching is derived from the act of turning ON or OFf  or going from 0 state to 1 or 1 state to 0 in order to change voltage levels. Switch could be pNormally Opened or Normally closed. Normally Open abbriviated to NO and Normally Closed NC. NO means current path is open against being flow from one contact or wire onto the other until it is switched to oposite state before current is allowed to flow while NC is the opposite in operation. NC allows current to flow from one contact unto the other and thereby allowing an action to be performed but switch off and disallow flow of current when it state is changed. Be careful to remember that switches has current ratings and should always be considered when making selection.

(NO and NC switch contact symbol)

TYPES OF SWITCH: Switches are of two major designs which are Toggle Switch (SPST, SPDT, DPST, DPDT and many more) and Momentery push button switch

Lamp: Lamps are generally an output devices used for indicating the presence of voltage or potential difference across in a circuit.  Lamps has voltage and power rating which are the operational rating capacity that determines the suitable condition in which it should be used. If used outside of rated values, blast or burnt out may occur which may cause injury to personnels and also damage the lamp. Lamps are also called BULB or simply indicator lamp.

Sensor: Sensor are input devices used in sensing, position, displacement, motion or movement. The term sensor is generally used which most are named according to the design or applications. They are made of inductive, or capacitive and or photo elements. Other names that are associated to them are photocell, proximity switch velocity sensor, temperature sensor, humidity sensor and many more. Sensors are also of discete and analog type and its selections is as well based on application. We will take time to devote time in exploring sensors and applications in another thread.

Relay: This is an electromagnetic switch that is also categorised as an output device. Designed to receive voltage at its coil terminals and then closes or opens its contacts as the designed may be. It contains a solenoid coil and many contacts, normally opened, normally closed or combination of both and sometimes with an indicator lamp to indicate its current operation status. They are mostly use for various control actions. They also comes in various sizes and pin numbers. They have voltage rating and contact current carry capacities.

Timer: Timer are electromagnetic relay with timing capability. They are usually used to manage time delay of event processes and aside the timing ability, it exibit all the primary function of a generic relay It comes in various type such as on delay, off delay, retentive, and pulse. The timing sequence also differs and settable according to application, such as milliseconds,  seconds, minutes, and hours.Timers are also with rated voltage and time range ratings.

Contactor: A contactor is an electromagnetic switch like a relay. It shares the same characteristics with a relay but are used for control and switching high power loads most especially Electric Motor and Heating circuits any other loads that consumes high current. Contactors had changed the way industrial load are being control because when it is integrated with an overload relay, it enhances safe protection of the load it is being control and has high switching accuracy with little arc effect.

Float switch: Float switch is an input device designed for use to receive feedback about liquid level in a Tank or Vessel in order to initial a fill or stop fill signal for starting of a punp or opening of valve that allow inflow of liquid or fluid into such Tank or Vessel. It sometimes come with  both NC and NO contacts or solely NC contact in tank empty condition.

 

Level probe: Level probe and Float switch are designed for the same level monitoring but the different is Float switch handles discrete signal processing while Level probe handles analog signal processing and provide accuracy in measurement while Float switch is only for control. Level probe generates analog output signal within the range of 4 to 20mA or 0 to 10V while Float switch generates digital signal of High or Low signal level. Level probes are calibrated or teached for accuracy while float switces are not.

Heater: heating element are output devices use to convert electrical signal into heat energy. This is used degenerating  heat on  surfaces which are use for further processes e.g thermoshrink tunnel, electric pressing iron, cooking hot plate and many more. It has lots of application. Some comes in cartridge form while some are wound on insulated rod.

Thermocouple: is an input device working on principle of bimetallic strip where two dissimilar metal are joined together and heat is applied, electric current will be setup by the heat. This advantage is made use of in thermocouple.  It is used to sense the amount of heat develop on a surface that is being heated up and then allow a corresponding current or voltage to be developed. There are two wires and three wires thermocouple.  They also comes in types such as PT100, type k, j, r, s and many more.

Push button switch: It is different in both design and operation when compared with the toggle switch as  earlier mentioned.  While a toggle switch remain on a position after being switched, a push button switch does not do that but instead provide only a momentary switching operation and immediately the finger is removed form it, it goes back to its initial position. They are mostly used in given start and stop signal in control operation. Some do have indicator lamp fitted to them to indicate their switching status and to have a feedback of the action being controlled.

Emergency button:  Emergency buttons are safety button used to bring a system or machine into an halt position during an emergency situation. That is, there is always a special consideration in the use of emergency button that is done during logic design that enable all moving and dangerous part of a systems or machine is designed to respond to the activation of emergency button. It alwasy have a mushroom head and when depressed, it must remain in the depressed position untill it is released intentionally.

Transformer: Transformer is a device used for changing voltage level for use in different electrical applications. A system can have more than three level of voltage, transformer is use to achieve that. They are either made to step-up voltage level or step-down voltage level. Step-up transformer is mostly used in power transmission and distribution while step-downtransformer is widely used in industries and control applications.

Power supply unit: PSU is used to provide a steady regulated dc voltage. They are commonly available in 24vdc but it is possible to get any voltage required order than 24v such as 3V, 5V, 6V, 9V, 12V and many more. PSU  is also known as Converters  It is a way of stepping down alternating current A.C. into direct current DC and the output is regulated and filtered from unwanted spike and fluctuations

Solid state relay: this relay is different from the relay mentioned earlier. Instead of coil and contacts, it makes use of thyristor which is capable of caring high current if a little amount of voltage between 5 to 30v dc is apply to its gate. Highly use in controlling heating elements with a perfect switching technique when reduces transient effect.

Fuse or circuit breaker: this are used to provide protection to components in electric circiut as well as personnel operating the equipment in case of any fault in any part of the circuit. Although Circuit breaker is gradually replacing fuse because of  response to fault and ease of switching back to operation while compared with the time spent in rewiring a fuse.

Electric Motor: electric motors are use to provide rotational or translational motion  useful in driving industrial machine. More on electric motor is covered in a separate page on this site.

Cable or Conductor: this is neither input or output component. It is use to provide connections or establish flow path between components.  They are also rated to carry different level of current and should be carefully selected before usage.

HMI: An abbreviation for Human Machine Interface also referred to as Man Machine Interface is an interface that operator and technician as well as equipment designers interact with in other to access machine functions and give command related to certain operating data or parameter. I is connected to the machine Processor and send information to and fro continuosly  regarding ongoing processes .

PLC: Programmable Logic Controller  is the central control device loaded with instructions and procedures that delicate the behaviour of plant and process equipment. All field devices such as switch, photocells, sensors and actuators are connected to the PLC as an input or output device.  The program loaded into it had been carefully coded to define certain operations